Automatic accompaniment device of an electronic musical instrument

ABSTRACT

An electronic musical instrument includes an automatic accompaniment device for automatically playing bass tones properly determined for the chords being played. A chord detector tells what chord is now being played. Responsive to the chord detection, a dc voltage generator generates a dc voltage representing the bass tone to be played. The dc voltage is supplied to a voltage controlled variable frequency oscillator which generates a bass tone signal having a frequency determined by the dc voltage. Thus produced bass tone is automatically gated by a tone gate in accordance with a rhythm pattern pulse generated by a rhythm pattern pulse generator.

United States Patent 191 Uchiyama [4 1 Mar. 5, 1974 22 Filed: June 23,1972

21 Appl. No.: 265,697

[30] Foreign Application Priority Data CHORD TONE GENERATORS 3,408,578 10/1968 Wolf et al. 331/113 R X 3,426,150 2/1969 Tygart 331/113 R X 3,538,804 11/1970 George 84/1.14 X 3,546,355 12/1970 Maynard 84/124 X 3,567,838 3/1971 Tennes et al. 84/1.l7 X

OTHER PUBLICATIONS J. Venn, A Simple Electronic Chord Organ, Electronic Engineering, July 1961 pages 421425.

Primary Examiner-Richard B. Wilkinson Assistant Examiner -N. Weldon Attorney, Agent, or Firm-Holman & Stern [57 ABSTRACT An electronic musical instrument includes an automatic accompaniment device for automatically'playing bass tones properly determined for the chords being played. A chord detector tells what chord is now being played. Responsive to the chord detection, a dc voltage generator generates a dc voltage representing the bass tone to be played. The dc voltage is supplied to a voltage controlled variable frequency oscillator v vhich generates a bass tone signal having a fret ueiicy determined by the dc voltage. Thus produced bass tone is automatically gated by a tone gate in accordance with a rhythm pattern pulse generated by a rhythm pattern pulse generator.

5 Claims, 7 Drawing Figures PAIENIED 3.795 7 55 sum 1'0: 5

F I G. I PRIOR ART RP I RHYTHM BS BASS ToNE GENERAToRs PPATTERN EE NEEATGR G] 3 K: ANDII ANDZI III" 'I' G T TONE c G E GATE i 6 2f AND22 G2 01 AND|2 E TONE "m J GATE D F ANDZE 0 I B I I I FXANDZI 2 4 I l CS K {9/ 2 2 CHORD I TONE C C TONE i GATE i GENERATORS 02 F I G; 2 C\D V? /VFO TG DC VOLTAGE CHORD CONTROLLED TONE DETECTOR VOLTAGE IQEIJIEN CY GATE OUT GENERATOR OSCILLATOR RHYTHM PATTERN PULSE GENERATOR PATENTED 5 SHEET 3 0F 5 FIG.4

OUT

N RI R FIG. 7

AIITOMATIC XCC'ISMPANIMENT DEVICE OF AN f ELECTRONIC MUSICAL INSTRUMENT BACKGROUND OF THE INVENTION The present invention relates generally to an electronic musical instrument and more particularly to a new and advanced automatic accompaniment device for automatically playing bass tones proper for the chords being played on the electronic musical instrument.

In general, it is customary and desirable in a musical performance effect on a musical instrument that a performer plays not only a melody but also a chord and bassaccompaniment on the musical instrument. However, such a performance, particularly of basses, is difficult for a beginner.

Accordingly, in an electronic musical instrument of known type, an automatic accompaniment device comprising a circuit such as that shown in FIG. 1 has been provided. In this Circuit, the operation of keyboard switches K causes one of AND circuits AND AND to operate, and the output from the particular AND circuit is applied to AND circuits AND AND thereby to derive proper bass tone signals out of the tone signals from bass tone generators BS to meet the chords being played. Then, the bass tone signals thus selected are applied to tone gates G,, G, L where the signals thus applied aregated in accordance with the signals from arhythm pattern pulse generator RP and finally reach'an output terminal When keys C, E and G are depressed, the key switches K of C, E and G are closed and a logical product condition is established in the AND circuit AND as a result of which the output of the AND circuit AND 1 is applied to the AND circuits AND and AND As a result, the AND circuit AND passes a bass tone signal of C from the bass tone generator BS to the tone gate G while the AND circuit AND- passes a bass tone signal of G to the tone gate G The tone gates G, and G are controlled by signals from the rhythm pattern pulse generator RP whereby the bass tone signals of the root note C and the fifth note G are applied to the output terminal 0,, respectively, at a time 1 and a time 3 according to the predetermined rhythm pattern.

on the other hand, the rhythm pattern pulse generator RP applys its signal toa tone gate G whereby the tone signals of C, E and G which have beensupplied from chord tone generators CS through key switches K of C, E and G are delivered to an output terminal 0, at a time 2 and a time 4. The outputs thus obtained at the output terminals 0 and O are then audibly produced through respective amplifiers and a loudspeaker. Thus, the performercan play a'melody accompanied by chords and basses, that is, even a beginner can perform an intricate musical piece.

However, since the above described conventional circuit is inevitably provided with bass tone generators including a number of tone generators in correspondence to the number of musical scale tones used, the circuit tends to be considerably complicated, and the cost of manufacturing a musical instrument having such a complicated circuit will be high.'

SUMMARY OF THE INVENTION electronic musical instrument in which a bass accompaniement is produced merely by the depressing of the keys that correspond to the component notes of a chord to be produced, and, therefore, even a beginner can obtain a good result in a complicate performance on the electronic musical instrument.

' A third object of the present invention is to providea new automatic accompaniment playing device of an electronic musical instrument in which bass tone generators of a type which is found in a conventional accompaniment device is eliminated whereby the new device is made much simpler in construction.

A fourth object of the present invention is to provide an automatic accompaniment device of an electronic musical instrument which is simplified in its entire organization, and is therefore appreciably advantageous in cost and manufacture.

The foregoing objects and other objects of the present invention will become more apparent from the following detailed description and the appended claims when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a block diagram illustrating a conventional automatic accompaniment playing device of an electronic musical instrument;

FIG. 2 is a block diagram showing a generic construction of the present invention;

FIG. 3 is a block diagram showing one embodiment of the present invention;

FIG. 4 is a circuit diagram illustrating a more specific example of the oscillator shown in FIG. 3;

FIG. 5 is also a block diagram illustrating another embodiment of the present invention;

FIG. 6 is a block diagram showing a further embodiment of the present invention; and

FIG. 7 is a circuit diagram showing in detail a control voltage generator included in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION As shown in FIG. 2, the automatic accompanying device according to this invention comprises: a chord detector CD for detecting a chord being played, a dc voltage generator VG connected to the chord detector CD and generating a dc voltage representing a bass tone proper for the detected chord, a voltage controlled variable frequency oscillator VFO Connected to the' dc voltage generator VG and oscillating a bass tone signal of a frequency determined by the dc voltage, a rhythm pattern pulse generator RP for generating pulses of pre determined rhythm patterns, and a tone gate TG connected to the'oscillator VFO and the pulse generator RP for gating the bass tone signal in response to the pulses. I

With reference now to FIGS. 3 and 4 there is shown one example of the automatic accompaniment playing device according to the present invention. This exam ple comprises: a chord detector including key switches K for every note (only C, E, G, F and Aare shown though) and AND Circuits AND AND each of which carries out its logical operation by the actuation of the connected key switches; AND circuits AN D AND which carry out their logical operations between the outputs of the AND circuits AND AND and the outputs ofa rhythm pattern pulse generator RP; a dc voltage generator including relays CX, GX which are activated by the outputs of the AND circuits AND AND anda resistor R on which several intermediate terminals (taps) are provided at predetermined intervals, whereby dc voltages of various values are obtained at the intermediate terminals when a dc current flows through the resistor R; a voltage controlled variable frequency oscillator VFO which, when a voltage is applied through the closed relay contact from the resistor R to the oscillator, serves to generate a bass tone signal whose frequency is determined by the dc voltage thus applied; a tone gate 6,, which gates the output of the oscillator VFO in accordance with the rhythm pattern pulses which are applied to the tone gate G through an OR circuit OR from the rhythm pattern pulse generator RP; and chord tone generators CS whose output are fed through key uct of the AND circuit AN D is established thereby indicating that the depressed chord is 'C and its output being fed to the AND circuits AND and AND The AND circuit AND is provided for the root note C of the chord 'C' while the AND circuit AND is provided for the fifth note G of the same chord. The AND circuits AND and AND g receive the signal from the AND circuit AND and the rhythm pattern pulses from the rhythm pattern pulse generator RP. The player of the electronic musical instrument provided with the above described device can be informed of the progression of the rhythm if for instance an indicator lamp is provided near the keyboard for facilitating the performance. 7

The rhythm pattern pulses are fed firstly to the AND circuit AND from an output terminal 1 of the rhythm pattern pulse generator RP, secondlyto the tone gate G, from an output terminal 2 of the generator RP, thirdly to the AND circuit AND from an output terminal 3 of thegenerator RP, and finally to the tone gate G from an output terminal 4 of the generator RP. Therefore, the AND circuit AND is first activated thereby to energize the relay CX, as a result of which the contact of the relay CX is closed. Since the'contact is connected to one of the intermediate terminals of the resistor type voltage divider R, a predetermined dc voltage representing a bass tone C is available at the intermediate tap. The dc voltage is applied, as a control signal, to the voltage controlled variable frequency oscillator VFO. As a result, the oscillator VFO generates a tone signal of a frequency for the bass note C (root for the chord C Similarly, generation of the rhythm pattern pulse at the output terminal 3 of the rhythm pattern pulse generator RP activates the AND circuit AND thereby to close the contact of the relay GX, as a result of whicha dc voltage representing a bass note G is applied to the oscillator VFO from another termiha] of the resistor R and the oscillator VFO in turn produces a tone signal of a frequency for the bass note G (fifth for the chord C). This signal is applied to the tone gate 0,.

As is indicated in FIG. 4, the oscillator may be, for instance, a combination of an astable multivibrator and a voltage amplifying circuit consisting of a Darlingtonconnected transistors Q, and Q. In this oscillator, its oscillating frequency is varied according to the variation of the voltage applied to a control'terminal V,

Referring to FIG. 3 again, the tone signals of the root note C and the fifth note G are derived from the output terminal 0 in accordance with the operation of the tone gate G l 7 On the other hand, since the rhythm pattern are fed to the tone gate G from the output terminals 2 and4 of the rhythm pattern pulse generator RP, the

chord signals delivered from the chord tone generators CS by depressing the keys C, E,and G is gated atthe tone gate G As a result, the chord note (C, E, G) signals are applied to at the output terminal 0 Thus, the performer can produce from the electronic musical instrument the root bass note, the fifthbass note, and chord notes beating'at the predetermined rhythm, merely by depressing the keys C, E, and G. The rhythms composed of these-tones can be optionally selected by rearranging the rhythm pattern pulses from I the rhythm pattern pulse generator RP.

In FIG. 5 there is shown another embodiment of the automatic accompaniment device according to the present invention, in which a pair of voltage controlled oscillators, the oscillating frequencies of which are in a certain ratio, are used as bass tone generators. In this example, two bass tone signals having predetermined frequencies are produced by the operation of keys,'and

the signals thus produced are gated, at tone gates, with the rhythm pattern pulses from the rhythm pattern pulse generator, so as to produce a desired bass accompaniment to the performance of a melody.

The device shown in FIG. 5 comprises: a chord de-' tector including key switches Kfor every note (only C, E,'G, A and F are shown though) and AND circuits AND AND .whose logical operations are carried out by the actuation of the connected key switches; a dc voltage generation including relays CX, FX which are activated by the operation of the AND circuits AND AND as a result of which the contacts of the relays are closed, and a resistor R on which several intermediate terminals (taps) are provided at predetermined intervals, whereby the dc voltages of various values are obtained at the terminals when a dc current flows through the resistor R; voltage controlled variable frequency oscillators VFO, and VFO each of which, when a voltage is applied to it from the resistor R through the closed relay contact, generates a bass tone signal whose frequency is determined by the thus applied dc voltage, the ratio of the two frequencies oscillated by the oscillators being 2:3; and a rhythm pat-' the pulses from the rhythm pattern pulse generator RP so as to gate the bass tone signal outputs from the oscilpulses lators VFO, and VFO and atone gate G,- which is operated by the outputs of the rhythm pattern pulse generator RP thereby to gate the chord tone signals delivered to the tone gate G, from the chord tone generators Cs through the key switches K.

The circuit shown in FIG. 4 can be employed as the oscillators VFO, and VFO As is apparent from the description set forth with reference to FIG. 4, the circuit comprises an astable multivibrator composed of transistors Q and Q, and a voltage amplyfying circuit composed of transistors Q, and 0,. In the oscillator, its oscillating frequency is varied according to the value of the dc voltage which is applied to the voltage input terminal V, and output of the oscillating frequency thus varied is applied to the output terminal OUT of the circuit.

When the key switches K of the notes C, E, and G (constituting a chord of C) are closed, the AND circuit AND, is activated as a result of which the relay CX is energized, and a predetermined voltage is then obtained at the resistor R. The voltage thus obtained is applied to the oscillators VFO, and VFO which in turn produce bass tone signals having frequencies determined by the dc voltage applied. In this connection, it should be noted that the ratio of the frequency of the oscillator VFO, to the frequency of the oscillator VFO,

is 2:3 ,that is, the-rafio showing'a relationship between a root note and a fifth note. In this example, since the root note is C and the fifth note is G, the bass tone signals generated by the oscillators have frequencies of the C note and the G note, respectively.

The outputs of the oscillators VFO,, and 'VFO, are applied to the tone gates G, and G respectively, and the tone gates G, and G, in turn carry out their gating operations according to the rhythm pattern pulses which are delivered from the output terminals 1 and 3 of the rhythm pattern pulse generator RP, respectively. As a result, first, the bass tone signal of the note C is delivered to an output terminal 0,, and then the bass tone signal of the note G is delivered to the same terminal 0,. I

On the other hand, the rhythm pattern pulses from the terminals 2 and 4 of the rhythm pattern pulse generator RP are supplied to the tone gate G and the rhythm pattern pulses thus supplied gate, at the tone gate G the chord tone signals which is delivered to the I tone gate G through the key switches K, and as a result the tone signals constituting the chord (C, E, G) appear at another output terminal 0 I Thus, the performer can produce the root bass note,

the fifth bass note, and chord'notes beating in the predetermined rhythm merely by depressing the key C, E and G. The rhythms composed of these tones can be optionally selected by rearranging the rhythm patterns of the rhythm pattern pulse generator RP.

With reference to FIGS. 6, there is shown a further example of the automatic accompaniment device according to the present invention, which also comprises a voltage controlled oscillator. In this example, two dc voltages respectively representing the frequencies for a root note and a fifth note are obtained by the operation of key switches, the thus obtained dc voltages are selectively applied to the oscillator according to the rhythm pattern pulses delivered from the rhythm pattern pulse generator thereby to produce'the bass tone signals of the root note and the fifth note, and chord tone signals are also gated by the rhythm pattern pulses. Thus, a desired bass and chord accompaniment is effected together with the performance of a melody.

More specifically, the example shown in FIG. 6 comprises: a chord detector including key switches K for every note (only C, E and G are shown though) and AND circuits AND,, which carries out its logical operation according to the operation of the connected key switches K; a dc voltage generator including relays CX, each of which is energized by the operation of the AND circuits AND,, whereby the contacts of the corresponding relay are closed, and a resistor R on which several intermediate terminals (taps) are provided at predetermined intervals, whereby the dc voltages of various values are obtained at the terminals when a current flows through the resistor R; and a rhythm pattern pulse generator RP.

This rhythm pattern pulse generator RP is preferably such that it can indicate the progression of the rhythm with the aid of, for instance, an indicator lamp which is provided in the vicinity of the keyboard of the electronic musical instrument so that the instrument player can operate the keys, referring to the indication of the lamps.

The above described, example further comprises: dc voltage gates CG, and CG, which carry out their gating operations according to the rhythm pattern pulses delivered from the rhythm pattern pulse generator RP thereby to selectively draw out the dc voltages from the resistor R; a voltage controlled variable frequency oscillator VFO which serves to generate the bass tone signal of a frequency determined by the dc voltages selectively delivered through the dc voltage gates CG, and CG,; a tone gate G the gating operation of which is caused by rhythm pattern pulses which are delivered through an OR circuit OR from the rhythm pattern pulse generator RP, whereby the bass tone signals from the oscillator VFO are supplied to an output terminal 0,; and a tone gate G the gating operation of which is caused by other rhythm pattern pulses from the rhythm pattern pulse generator RP thereby to gate the chord tone signals which are delivered to the tone gate G through the closed key switches K from the chord tone generators CS and to send the chord tone signals thus gated to another outputterminal 0 The dc voltage generator, which is a part of FIG. 6, including the resistor R and the relay contacts, and serving to obtain the voltages to be used for determining the frequency of the oscillator VFO, is further illustrated in detail in FIG. 7. When a current flows through the resistor R from a dc. source, it produces at the intermediate terminals of the resistor R the voltages that are preselected suitable for determining the frequency of the oscillator VFO. The resistor R is provided with two groups of terminals, namely, one group of terminals going to the dc. voltage gate CG, and the other group of terminals going to the dc voltage gate CG Therefore, the voltages produced at the terminals are applied to the oscillator VFO through the dc voltage gate CG, or CG,. 7

The circuit shown in FIG. 4 can be employed as one example of the oscillator VFO. As is described before, the circuit has a voltage amplifying circuit comprising the transistors Q, and Q and an astable multivibrator comprising the transistors Q and Q.,.

When the key switches K of the notes C, E, and G (constituting chord of C) are closed, the AND circuit AND,, is caused to carry out its logical operation, as a result of which the relay CX is energized thereby to close its contacts for C and G representing voltages. Owing to these contact closures, the different dc voltages for the root note C and the fifth note G are applied to the gates CG, and CG respectively.

The gate CG, and CG, carry out their gating operations with rhythm pattern pulses applied from the rhythm pattern pulse generator RP to them. First, the gate CG, is opened by the rhythm pattern pulse arriving from a terminal 1 of the rhythm pattern pulse generator RP. At a predetermined time interval thereafter, the gate C6 is opened by a rhythm pattern pulse arriving from another terminal 3 of the rhythm pattern pulse generator RP. Accordingly, the variable frequency oscillator VFO first receives a dc voltage which has a value to produce the root note C, thereby to generate the bass tone signal of the note C, and next receives another dc voltage which has a value to produce the fifth note G, thereby to generate the bass tone signalof the note G.

The bass tone signals thus generated are applied to the tone gate 6,. The gate G in turn carries out its gating operation according to the rhythm pattern pulses from the rhythm pattern pulse generator RP, and owing to this gating operation, the bass tone signals from the oscillator VFO is applied to the output terminal On the other hand, the rhythm pattern pulses from the other output terminals 2 and 4 of the rhythm pattern pulse generator RP are applied to the tone gate G,., as a result of which the gate G is opened at time points 2 and 4. This means that the chord tone signals are delivered to the output terminal 0 through the key switches K from the chord tone generators CS.

Thus, the performer can produce theroot bass note, the. fifth bass note, and the chord notes at predetermined rhythms, merely by depressing the keys C, E, and G. The rhythms composed of these tones can be optionally selected by rearranging a rhythm patterns of the rhythm pattern pulse generator RP.

While a-few embodiments of the present invention have been illustrated and described in detail, it is particularly understood the present invention is not limited thereto or thereby.

I claim:

1. In an electronic musical instrument having a plurality of key switches wherein actuation of each key switch acts to generate a different single note of a musical scale, and automatic accompanying device therefor, said device comprising:

-a voltage'means, said key switches being connected to said voltage means; chord detectormeans coupled to said individual key switches for monitoring designated combinations of notes being played to detect the presence of different chords, said chord detecting means comprising a plurality of AND circuits connected to. said key switches as chord detecting logics, said chord detector means providing an output indicative of said selected chord;

a D.C. voltage generator means coupled I to said chord detector means for generating a D.C. voltage having a level representative of said detected chord, said D.C. voltage generator comprising a source of D.C. current, a plurality of relays connected'to and energized by said AND circuits and a voltage dividing circuit having a resistor coupled to said source of D.C. current and adapted to proa rhythm pattern pulse generator means for generating pulses of predetermined rhythm patterns, and

a tone gate means connected to said oscillator means and said pulse generator means for gating said generated bass tone signal in response to said pulses. 2. An automatic accompaniment device as claimed in claim 1 in which said voltage controlled variable frequency means comprises a first oscillator and a second oscillator, the first oscillator generating a bass tone signal having a frequency of the root note for the detected chord, the second oscillator operating simultaneously with the first oscillator and generating a base tone signal having a frequency of the fifth note for the detected chord, the first and the second oscillator being connected respectively to a pair of tone gates which gates the signals, applied thereto from the first and the second oscillator, in accordance with the rhythm pattern pulses from the rhythm pattern pulse generator.

3. An automatic accompaniment device instrument as claimed in claim 1 in which said variable frequency oscillator means comprises an astable multivibrator and a voltage amplifying circuit connected to said astable multivibrator.

4. In an electronic musical instrument having a plurality of key switches wherein actuation of each'key switch acts to generate a different single note of a musical scale, and automatic accompanying device therefor, said device comprising: 7

a voltage means, said key switches being connected to said voltage means;

chord detector means coupled to said individual key switches for monitoring designated combinations of notes being played to detect the presence of different chords, said chorddetecting means comprising a plurality of AND circuits connected to said key switches as chord detecting logics, said chord detector means providing an output indicative of said selected chord;

a D.C. voltage generator means coupled to said chord detector means for generating a D.C. voltage having a level representative of said detected chord, said D.C. voltage generator comprising a source of D.C. current, a plurality of relays connected to and energized by said AND circuits and a voltagedividing circuit having a resistor coupled to said source of D.C. current and adapted toproduce step-down voltages at intermediate terminals provided on said resistor upon application of a D.C. current thereto, and contacts connected to said terminals, whereby predetermined voltages age generator for generating a bass tone signal proper for the detected chord, said bass tone signal being at a frequency determined by said D.C. voltage;

v a rhythm pattern pulse generator means for generating pulses of predetermined rhythm patterns, and a tone gate means connected to said oscillator means and said pulse generator means for gating said generated bass tone signal in response to said pulses, and wherein said plurality of AND circuits comprises a first and a second AND circuit group, the first AND circuit group being connected to said key switches which correspond to the notes of a chord thereby carrying out logical operation thereof, the second AND circuit group being connected to and operated by the output of the first AND circuit group and the outputs of the rhythm pattern pulse generator, and wherein said plurality of relays are connected to and energized by the second AND circuit group.

5. In an electronic musical instrument having a plurality of key switches wherein actuation of each key switch acts to generate a different single note of a musical scale, and automatic accompanying device therefor, said device comprising:

a voltage means, said key switches being connected to said voltage means;

chord detector means coupled to said individual key switches for monitoring designated combinations of notes being played to detect the presence of different chords, said chord detecting means comprising a plurality of AND circuits connected to said key switches as chord detecting logics, said chord detector means providing an output indicative of said selected chords;

a D.C. voltage generator means coupled to said chord detector means for generating a D.C. voltage having a level representative of said detected chord, said D.C. voltage generator comprising a source of D.C. current, a plurality of relays connected to and energized by said AND circuits, and a voltage dividing circuit having a resistor coupled to said source of D.C. current and adapted to produce step-down voltages at two groups of intermediate terminals provided on said resistor upon application of a D.C. current thereto, and contacts connected to said terminals, whereby predetermined voltages are selectively obtained by means of said contacts being actuated by said energized relays;

a voltage controlled variable frequency oscillator means for generating a bass tone signal proper for the detected chord, said bass tone signal being at a frequency determined by said D.C. voltage;

a rhythm pattern pulse generator means for generating pulsesvof predetermined rhythm patterns, and a tone gate means connected to'said oscillator means and said pulse generator means for gating said generated bass tone signal in response to said pulses;

and wherein a voltage gate circuit is connected to said rhythm pattern pulse generator. and said D.C. voltage generator, said gate circuit providing a gating operation which is carried out in accordance with the rhythm pattern pulses from said rhythm pattern pulse generator to thereby gate said D.C. voltage supplied from said D.C. voltage generator, said gate circuit further providing an output signal which is applied to the voltage controlled variable frequency oscillator means. 

1. In an electronic musical instrument having a plurality of key switches wherein actuation of each key switch acts to generate a different single note of a musical scale, and automatic accompanying device therefor, said device comprising: a voltage means, said key switches being connected to said voltage means; chord detector means coupled to said individual key switches for monitoring designated combinations of notes being played to detect the presence of different chords, said chord detecting means comprising a plurality of AND circuits connected to said key switches as chord detecting logics, said chord detector means providing an output indicative of said selected chord; a D.C. voltage generator means coupled to said chord detector means for generating a D.C. voltage having a level representative of said detected chord, said D.C. voltage generator comprising a source of D.C. current, a plurality of relays connected to and energized by said AND circuits and a voltage dividing circuit having a resistor coupled to said source of D.C. current and adapted to produce step-down voltages at intermediate terminals provided on said resistor upon application of a D.C. current thereto, and contacts connected to said terminals, whereby predetermined voltages are selectively obtained by means of said contacts being actuated by said energized relays; a voltage controlled variable frequency oscillator means connected to said contacts of said D.C. voltage generator for generating a bass tone signal proper for the detected chord, said bass tone signal being at a frequency determined by said D.C. voltage; a rhythm pattern pulse generator means for generating pulses of predetermined rhythm patterns, and a tone gate means connected to said oscillator means and said pulse generator means for gating said generated bass tone signal in response to said pulses.
 2. An automatic accompaniment device as claimed in claim 1 in which said voltage controlled variable frequency means comprises a first oscillator and a second oscillator, the first oscillator generating a bass tone signal having a frequency of the root note for the detected chord, the second oscillator operating simultaneously with the first oscillator and generating a base tone signal having a frequency of the fifth note for the detected chord, the first and the second oscillator being connected respectively to a pair of tone gates which gates the signals, applied thereto from the first and the second oscillator, in accordance with the rhythm Pattern pulses from the rhythm pattern pulse generator.
 3. An automatic accompaniment device instrument as claimed in claim 1 in which said variable frequency oscillator means comprises an astable multivibrator and a voltage amplifying circuit connected to said astable multivibrator.
 4. In an electronic musical instrument having a plurality of key switches wherein actuation of each key switch acts to generate a different single note of a musical scale, and automatic accompanying device therefor, said device comprising: a voltage means, said key switches being connected to said voltage means; chord detector means coupled to said individual key switches for monitoring designated combinations of notes being played to detect the presence of different chords, said chord detecting means comprising a plurality of AND circuits connected to said key switches as chord detecting logics, said chord detector means providing an output indicative of said selected chord; a D.C. voltage generator means coupled to said chord detector means for generating a D.C. voltage having a level representative of said detected chord, said D.C. voltage generator comprising a source of D.C. current, a plurality of relays connected to and energized by said AND circuits and a voltage dividing circuit having a resistor coupled to said source of D.C. current and adapted to produce step-down voltages at intermediate terminals provided on said resistor upon application of a D.C. current thereto, and contacts connected to said terminals, whereby predetermined voltages are selectively obtained by means of said contacts being actuated by said energized relays; a voltage controlled variable frequency oscillator means connected to said contacts of said D.C. voltage generator for generating a bass tone signal proper for the detected chord, said bass tone signal being at a frequency determined by said D.C. voltage; a rhythm pattern pulse generator means for generating pulses of predetermined rhythm patterns, and a tone gate means connected to said oscillator means and said pulse generator means for gating said generated bass tone signal in response to said pulses, and wherein said plurality of AND circuits comprises a first and a second AND circuit group, the first AND circuit group being connected to said key switches which correspond to the notes of a chord thereby carrying out logical operation thereof, the second AND circuit group being connected to and operated by the output of the first AND circuit group and the outputs of the rhythm pattern pulse generator, and wherein said plurality of relays are connected to and energized by the second AND circuit group.
 5. In an electronic musical instrument having a plurality of key switches wherein actuation of each key switch acts to generate a different single note of a musical scale, and automatic accompanying device therefor, said device comprising: a voltage means, said key switches being connected to said voltage means; chord detector means coupled to said individual key switches for monitoring designated combinations of notes being played to detect the presence of different chords, said chord detecting means comprising a plurality of AND circuits connected to said key switches as chord detecting logics, said chord detector means providing an output indicative of said selected chords; a D.C. voltage generator means coupled to said chord detector means for generating a D.C. voltage having a level representative of said detected chord, said D.C. voltage generator comprising a source of D.C. current, a plurality of relays connected to and energized by said AND circuits, and a voltage dividing circuit having a resistor coupled to said source of D.C. current and adapted to produce step-down voltages at two groups of intermediate terminals provided on said resistor upon application of a D.C. current thereto, and contacts connected to said terminals, whereby predetermined voltageS are selectively obtained by means of said contacts being actuated by said energized relays; a voltage controlled variable frequency oscillator means for generating a bass tone signal proper for the detected chord, said bass tone signal being at a frequency determined by said D.C. voltage; a rhythm pattern pulse generator means for generating pulses of predetermined rhythm patterns, and a tone gate means connected to said oscillator means and said pulse generator means for gating said generated bass tone signal in response to said pulses; and wherein a voltage gate circuit is connected to said rhythm pattern pulse generator and said D.C. voltage generator, said gate circuit providing a gating operation which is carried out in accordance with the rhythm pattern pulses from said rhythm pattern pulse generator to thereby gate said D.C. voltage supplied from said D.C. voltage generator, said gate circuit further providing an output signal which is applied to the voltage controlled variable frequency oscillator means. 